Question

Thenard blue is
A. $Cu\left( {N{H_3}} \right)S{O_4}$
B. $CoA{l_2}{O_4}$
C. ${K_2}Fe\left[ {Fe{{\left( {CN} \right)}_6}} \right]$
D. $F{e_4}{\left[ {Fe{{\left( {CN} \right)}_6}} \right]_3}$

Answer 1

Hint: In these types of questions you should know what type of compounds Thenard is, its properties, how it has formed and at what suitable temperature it is formed remember these facts to find the correct option.

Complete step-by-step answer:
The compound Thenard blue mentioned in a question first let’s find out what this compound is and how it is formed.
Thenard blue is also known as Cobalt blue, it is a blue color pigment, this compound is made by finely ground $CoO$ and $A{l_2}{O_3}$at ${1200^ \circ }C$temperature. Here, $CoO$ is Cobalt Oxide and $A{l_2}{O_3}$ is Aluminum oxide. Thus, the compound formed is $CoA{l_2}{O_4}$.
Hence, the correct option is B.

NOTE: We used a term Cobalt blue which is extremely stable pigment. If we inhale or ingest this pigment is toxic. Cobalt blue has been used in ceramics, jewelry and paint as a coloring agent. Potters that do not take sufficient precautions when cobalt blue is used may succumb to cobalt poisoning.